1. Field of the Invention
The present invention is generally directed to remote control switches. More particularly, the present invention is directed to remote control switches, such as lighting contactors that are electromagnetically-operated, mechanically held switch. One such remote control switch is disclosed in U.S. Pat. No. 4,430,579 which is herein entirely incorporated by reference and to which the reader is directed for further information. Such switches may be utilized in a wide range of different applications and are typically used for controlling lighting, heating and other like or similar type loads. A conventional remote control switch comprises essentially a circuit disconnect device that may be operated from one and/or a plurality of separate or interrelated control stations. Such control stations may be spread out over an area such as locally dispersed within a room, across a building, or some other remotely located area. However, aspects of the invention may be equally applicable in other scenarios as well.
2. Description of Related Art
A general diagram of a conventional remote control electromechanical switch circuit 10 is illustrated in FIG. 1. As can be seen from FIG. 1, remote control electromechanical switch circuit 10 comprises a primary switch 12 coupled to a remote control switch 14. Primary switch 12 comprises mechanical contacts 40. Primary switch 12 is coupled to AC line 28 and to an input of remote control switch 14. Mechanical contacts 40 of primary switch 12 may be switched or positioned in either an up position 30 or a down position 32. FIG. 1 illustrates the mechanical contacts 40 of switch 12 in an up position 30. Primary switch 12 is utilized to provide AC power from AC line 28 to remote control switch 14. AC line 28 may comprise a conventional industrial AC line having 115/220 VAC, 50/60 Hz, however, the primary switch 12 may be utilized with other power grids as well.
Remote control switch 14 comprises a first set of contacts 16, a diode 20, a solenoid 24, and a second set of contacts 26. The first set of contacts 16 is coupled to an output of primary switch 12 whereas the second set of contacts 26 powers a load 27.
Both solenoid control switch 36 and power load switch 38 are physically linked to solenoid 24. Solenoid control switch 36 and a power load switch 38 have certain stable, mechanically locked positions and certain of these positions are illustrated in FIG. 1. For example, solenoid control switch 36 is illustrated in a down stable position 34 while power load switch 38 is illustrated in an up or open stable position 26a. In this up or open position 26a, load 27 remains unconnected
AC line is continuously coupled to the primary switch 12. When primary switch contact 40 moves from the up position 30 to the down position 32, the solenoid 24 energizes and thereby moves both of the physically linked contacts 16 and contacts 26 until a closed solenoid position 26b is reached. In this closed solenoid position 26b, the solenoid 24 is disconnected from the line 28 via open contacts 16 in position 36. Operation and control of remote control switch 14 may be explained in detail with reference to the various timing diagrams illustrated in FIGS. 2(a-e).
For example, FIG. 2a illustrates an exemplary AC line voltage 28 that may be applied to primary switch 12 and that is eventually applied at node 18 of mechanical remote control circuit 10. Node 18 resides after contact 16 but before diode 20 in FIG. 1. Once AC line voltage 28 appears at diode 20 (such as at point 28a in FIG. 2c diode 20 conducts only a positive half wave of the applied AC power to solenoid 24. Consequently, this half wave voltage of AC voltage 28 will be applied to solenoid control switch 36 and is input to diode 20. In one arrangement of such a remote control switch 14, a one complete half wave of incoming AC voltage 28 (FIG. 2a) is sufficient to complete a switch transition. Such a switch transition may typically occur on the order of approximately from about 5-7 milliseconds to about 10 milliseconds. A customer load 27 will be connected via power load switch 38 once the second set of contacts 26 of remote control switch 14 are completed or made.
In a first stable position, the contacts 40 of primary switch 12 reside in the upper position 30 and the contacts 26 of the solenoid control switch 38 also resides in the upper position 26a as illustrated in FIG. 1. When primary switch 12 is first activated (i.e., when the contacts 40 of switch 12 are switched from the upper position 30 to lower position 32), a first positive half wave of AC input voltage 28 (such as at point 28a in FIG. 2a) passes diode 20 and energizes the solenoid 24. The energized solenoid 24 pulls in both sets of mechanical contacts 26 and 16, contacts 26 then move to a second stable position 26b and thereby provides power to the coupled load 27.
The first positive half wave at point 28c of AC power 28 (FIG. 2a) toggles both groups of contacts (i.e., solenoid control switch 16, optional auxiliary contacts (not shown) and power load switch 26). When solenoid control switch 16 is first toggled, solenoid 24 is mechanically disconnected from AC input voltage 28. Remote control switch 14 has now moved into its second stable position 26b and remains in this second stable position 26b until primary switch 12 is again actuated.
There are certain concerns that may arise with conventional mechanical switching circuits, such as the conventional circuit 10 illustrated in FIG. 1. For example, one concern relates to certain mechanical contact bounce, or contact “chattering” that may occur with the contacts 40 of primary switch 12. For example, because moving contacts 40 of primary switch 12 has a certain mass associated with its structure as well as a certain spring rate with low damping, contacts 40 tend to bounce as they make and break a completed circuit. That is, when these normally open pair of contacts 40 are closed, these contacts 40 often tend to initially come together (“make”) and then tend to bounce/chatter off one another several times (“break”) before the contacts finally come to rest or remain in a desired (i.e., closed) stable position. Such contact bounce may result in unwanted contact arcing and this may unduly limit the operational lifetime of the contacts of primary switch. For example, certain consequences of this making and breaking of the primary switch contacts 40 may be illustrated in the timing diagram in FIGS. 2b-2e, and importantly the timing diagram 50 illustrated in FIG. 2b. 
As shown in timing diagram 50 illustrated in FIG. 2b, when the contacts 40 of the primary switch 12 are in the first up position 30 and then when the contacts 40 are switched to closed or down position 32, contacts 40 of primary switch 12 have a tendency to remain in an un-stable position, somewhere between the contact open position 30 and the contact closed position 32. The contacts will eventually, however, reside in the down position 32 but only after a certain period of time t1 44. Depending on certain aspects of switch construction, mechanics, and design, such mechanical contact bounce can last up to approximately 15 milliseconds to 20 milliseconds. That is, as illustrated in FIGS. 2b and 2c, contact bounce Tcb 43 may last from t0 42 to t1 44. For further information on such mechanical bounce and its related issues, the reader is directed to http://www.elexp.com/t_bounc.htm which is herein entirely incorporated by reference and to which the reader is directed for further information.
Such contact bounce is normally undesired. For example, such contact bouncing often tends to interrupt current flow, as such current flow is eventually applied to energize a solenoid of a remote control switch, such as solenoid 24 illustrated in FIG. 1. For example, a timing diagram 56 of such a potentially problematic current flow is illustrated in FIG. 2c. FIG. 2c illustrates a timing diagram 56 that represents the current available at node 18 directly before diode 20 as contacts 40 go through a bouncing state, transitioning between the up position 30 and the closed positions 32 illustrated in FIG. 2b. As can be seen from timing diagram 56, contact bounce results in intermittent power or intermittent energy 52 during the one period from t0 42 to t1 44. The intermittent power or energy 52 is available at diode 20 and before solenoid 24. Contact bounce/chatter can adversely affect current flow and can also cause undesired contact arcing.
Consequently, as the timing diagram 58 of FIG. 2d illustrates, there is limited or insufficient energy 60 available at node 18 for solenoid 24 to make a complete mechanical transition from its initially open stable state 26a to a desired closed stable state 26b. Sufficient energy 62 to make such a transition will be available only once the electrical bounce or chatter of contacts 40 of switch 12 has subsided. FIG. 2d illustrates a timing diagram of the varying energy that will be present after the diode 20 at node 22 but before solenoid 24. Therefore, as illustrated in FIGS. 2d-e, prior to time t2 70, there is insufficient energy to complete a mechanical transition of second set of contacts 26. As illustrated in FIG. 2e, during contact bounce as illustrated in FIGS. 2b and 2c, there is incomplete mechanical transition 66 that occurs during switch bounce illustrated in FIG. 2b. It is only after a certain period of time that takes into account contact bounce that there is a sufficient amount of energy available so that a complete mechanical transition 68 can occur. Consequently, the control of remote control switch 14 illustrated in FIG. 1 tends to be inconsistent. This is true in part since the primary switch 12 may be switched at any time during the line voltage 28. For example, under certain ordinary operating conditions, the remote switch completes its transition within a half of period of the line voltage such as within about 8.33 ms for 60 Hz AC line voltage and about 10 ms for 50 Hz AC line voltage.
Therefore, when a duration of contact bounce or chatter is critical to a switch transition time, remote control switch 14 will not have enough stored energy to make a reliable transition between an initial open state and a desired closed state. Therefore, as contacts 40 are loaded, contacts 40 will have a tendency to experience electrical chatter. This chatter may occur because solenoid 24 is not able to solidly transition from its open state to a closed state during this switch transition time.
One technique that has been utilized in an attempt to reduce or eliminate such mechanical contract bounce is to provide a circuit that introduces a solid state switch between the primary switch 12 and the remote control switch 14. For example, FIG. 3 illustrates such a solid state based solenoid control circuit 13.
However, even such typical electronic solid state switch designs present certain operating and control limitations. For example, a solid state switch 48 coupled between a mechanical primary switch 12 and remote control switch 14 eliminates contact bouncing. However, one such concern with such an electronic solid state switch construction relates to what occurs if AC power is applied after solenoid 24. That is, if AC power is applied to solenoid 24 after the beginning of a positive half wave of input AC voltage. As with the use of an electromechanical primary switch 12, there may be insufficient energy to complete a switch transition. This concern regarding insufficient switch transition energy and the resulting synchronization issues with utilizing a solid state based switch raised by these concerns may be generally illustrated in the various timing diagrams presented as FIGS. 4(a-e).
Returning to FIG. 3, FIG. 3 illustrates a solid state switch 48 coupled to a primary switch 12 and remote control switch 14. Such a solid state switch 48 may comprise different solid state semiconductors such as triacs, MOSFETs, IGBTs, SCRs, as well as other like solid state components. In this exemplary arrangement, solid state switch 48 comprises a first triac 46 and a second triac 54 however other alternative arrangement may also be utilized. Also in this exemplary arrangement, a mechanical primary switch 12 (with potential contact bounce limitations) is utilized for solenoid control. In an up position 30 of a primary switch 12, the first triac 46 will be in an ON state while the second triac 54 will be in an OFF state. FIGS. 4(a-e) illustrate various timing diagrams for the solid state based switch circuit 13. For example, FIG. 4a illustrates a timing diagram of the AC line voltage 28 and FIG. 4b illustrates a timing diagram 80. FIG. 4c illustrates a timing diagram 88 that represents a voltage available at node 18 directly before diode 20 as solid state switch 48 transitions from an OFF state to an ON state. Transitioning between the OFF state and the ON state illustrated in FIG. 4b. As can be seen from the timing diagram 88 in FIG. 4c, even for the solenoid control circuit 13 utilizing a solid state switch 48, depending on where during the AC line cycle 28 that the solid state switch 48 transitions between its ON and OFF state (and where the primary switch 12 transitions between its up and down position (as shown in this example, transition occurs at point 28d in FIG. 4a), there may still be insufficient or intermittent power or energy 102 available at diode 20. Therefore, there will be insufficient energy to drive solenoid 24. Consequently, as the timing diagram 104 of FIG. 4d illustrates, even when utilizing a solid state switch 48, there will often be insufficient energy available at node 18 for solenoid 24 to make a complete mechanical transition 111 from its closed state to the desired open state. Sufficient energy to make such a complete mechanical transition will be available only once the electrical bounce or chatter of contacts 40 of switch 12 has subsided. FIG. 4d provides a timing diagram illustrating the varying amount of energy that will be present after the diode 20 at node 22 but before solenoid 24.
Therefore as can be illustrated in the various timing diagrams illustrated in FIGS. 4d-e, prior to time t1 71, there is insufficient energy 102 to complete a mechanical transition of second set of contacts 26. As can be seen from FIG. 4e, it is only after time t1 71 that a complete mechanical transition 111 can occur. Consequently, as with the mechanical control switch illustrated in FIG. 1, control of the remote control switch 14 illustrated in FIG. 3 even utilizing solid state switch 48 will tend to be inconsistent.
There is, therefore, a general need for a solenoid control circuit that provides for a controlled solenoid circuit that can consistently provide a sufficient amount of energy for contact closure. Also, there is a general need for a controlled solenoid circuit that reduces or even eliminates contact bounce or chatter. There is also, therefore, a general need for a control circuit that reduces certain undesired contact heating, contact arcing, and/or contact wear that can oftentimes occur during unwanted contact bounce.